Screwing element

ABSTRACT

In a screwing element ( 1 ) for accommodation of a fastener head ( 5 ) of a fastener ( 6 ) there are provided jaws ( 3, 4 ) for seizing the fastener head. The jaws ( 3, 4 ) can be axially inserted into or withdrawn from the holder ( 2 ), wherein the jaws in the withdrawn position can be pivotably forced apart into open position. At their free end the jaws are provided with incisions ( 15, 16 ) and, adjoining these, with gripper-like parts ( 17, 18 ) jutting outwardly toward the central axis for the purpose of engaging mechanically and/or frictionally with the fastener head ( 5 ) from behind.

The invention relates to a screwing element for holding and for forciblyturning a fastener, with a plurality of jaws, which are disposed insuccession in circumferential direction for seizing the fastener,wherein the jaws engage in a tubular holder and, in cooperation withthis holder, in a first end position can be forced radially apart forthe purpose of holding the fastener, and in a second end position can beradially squeezed toward each other by mechanical action of the holderin response to application of axial and/or radial force.

Such screwing elements have become known in a plurality of differentembodiments. As a rule, such screwing elements have a recess foraccommodating the fastener head, wherein the recess as viewed in axialdirection has a cross section matched to the cross section of thefastener head, so that torque can be transmitted while the fastener isbeing driven in. Accordingly a fastener is guided axially with its headin the recess in such a screwing element. Spring-loaded pins or ballscan also be disposed, for example, to prevent the head of a fastenerfrom slipping out spontaneously after it has been inserted in thescrewing element. Thus captive protection is achieved at leasttemporarily. If such a fastener is to be driven into a correspondingworkpiece, however, then axial force transmission is also needed, and soappropriate stop elements must in turn be provided in a screwing elementin order to limit movement toward the screwing element. Since thediameter of the threaded shank of the fastener is normally much smallerthan the diameter of the fastener head, it is usually even necessary toprovide centering for the shank, in order that proper setting of thefastener can be achieved at all.

The object of the present invention is therefore to provide a screwingelement of the type mentioned in the introduction, with which element afastener head or portions of a fastener head can be immobilized in axialdirection during setting of a fastener, specifically until the fasteneris finally tightened.

This object is achieved according to the invention by the fact thatincisions or recesses are formed on the free end region of the jaws formechanical and/or frictional accommodation of a fastener head, and thatgripper-like parts jutting outwardly toward the central axis or directedaway therefrom are formed on the free end of the jaws, adjoining theincisions or recesses, for the purpose of additional mechanical and/orfrictional seizing of portions of the fastener head.

By means of the screwing element according to the invention, thefasteners to be inserted can be clamped in the region of the fastenerhead in such a way that they can no longer be moved in axial direction,and that they remain axially aligned with the screwing elementthroughout the entire setting process and thus permit optimal driveaction by a driving tool. Because of the radial squeezing effect ofcorresponding jaws, not only can the fastener head be seized exactly,but also corresponding engagement with the fastener head from behind ispossible without the need for additional stop elements and studs orballs which spring back under spring loading.

To achieve particularly good alignment between screwing element andfastener and to permit exact clamping of the fastener head, it isprovided that the incisions, recesses or the like on the jaws correspondat least approximately to the cross section of the rim region of thefastener head to be seized or of a shoulder formed thereon. The screwingelement or the jaws thereof can be adapted to a specially formedfastener, to the effect that a highly special screwing element, withwhich the fasteners can also be optimally set, is available for a givenindividual application.

In order to achieve proper torque transfer during a boring process, athread-forming process or merely during the process of driving in afastener, it is proposed that, in the region of the incisions, recessesor the like or adjoining these at offset position in axial direction oreven on the gripper-like parts or openings or profiled structures, therebe provided extensions of a tool for acting on a fastener head or onportions thereof. In this way optimal torque transfer is achieved inaddition to the mechanical holding effects of the jaws, by the fact thatextensions of a tool are provided precisely in the affected regions ofthe jaws.

In this connection it is advantageous for the jaws to be spring-loadedtoward their open position. Thus, when the jaws are in open position,they are always pivoted away from each other, and so no problems of anykind occur for insertion of the next fastener.

To ensure that the jaws do not come into contact with the surface of theworkpiece until a fastener has just been finally set, it is providedthat the thickness of the gripper-like portions viewed in axialdirection of the screwing element is smaller than the axial length of afastener-head portion which on the shank side adjoins a shoulder formedcircumferentially on the fastener head. In all cases, therefore, thelowest edge of the jaws and thus of the gripper-like parts is stilldisposed at a corresponding distance from the surface of the workpiece,and so the fastener head can be immobilized until setting has just beencompleted, without scratching of the workpiece surface.

A simple structural variant provides that, on the inside of the holderand/or on the outside surface of the jaws, there are formed cammingsurfaces which taper sharply relative to the central axis, wherein thejaws can be squeezed toward each other by the camming surfaces inresponse to being forced axially into the holder. In this way forcedclosing of the jaws can be achieved with simple means, specificallymerely by pushing the fastener axially inward, wherein the fastener headacts appropriately on the jaws. If axial pressure is additionallyexerted by the driving tool during the setting process, the sharplytapering camming surfaces generate an additional radial component offorce, thus clamping the fastener head even more forcefully during theprocess of setting of the fastener.

To ensure that satisfactory force transmission can occur, it isadvantageous for sharply tapering camming surfaces to be provided onboth the holder and on the jaws.

In a particular structural variant, it is further provided that the jawsare equipped at their ends protruding into the tubular holder withradially inwardly directed toes, which engage in a radiallycircumferential groove of a stud that is axially slidable in thescrewing element and can be fixed in a plurality of latching positions,wherein this stud can be positioned together with the jaws by the actionof axial pushing or pulling thereon.

In this way the jaws are secured not only in axial direction and thusheld captively, but thereby can also be brought into a specific open endposition and closed end position in cooperation with the stud. Since thejaws in one of their end positions remain in the closed position, thefastener head cannot fall out downward again, even during assembly,after insertion between the jaws. In this precise connection it isadvantageous for the stud to be fixed latchingly at least in the two endpositions of the jaws.

For this purpose it is proposed that the stud be provided with at leasttwo latching positions formed by circumferential grooves, wherein aspring-loaded pin or a ball which engages in the correspondingcircumferential groove is held against the tubular holder. Thereby thereare created secure latching positions, which prevent inadvertentmaladjustment of the jaws in the open position and in the closedposition.

To achieve optimal cooperation between the stud and the jaws cooperatingmechanically or frictionally with the stud, it is proposed that thestud, on its portion adjoining the groove for engagement with the toesformed on the jaws, be adapted to the inside cross section of the jawsin closed condition, wherein the transition between the groove and theend part of the stud and the corresponding regions of the jaws arespherically convex. This ensures not only exact guidance between thestud and the jaws, but also exact pivoting capability without tiltingand thus without operating disturbances for the screwing element.

Further technical possibilities are achieved by the construction of ascrewing element according to the invention. In one particularembodiment, for example, a tool for an internal drive can be formed atthe center between the jaws. In such a case the jaws are neededpractically only for immobilizing and axially aligning the fastener,whereas the motive power for driving in can be provided via an internaldrive. In such a construction it is particularly advantageous for thetool for an internal drive to be formed or disposed at the free end ofthe stud which is slidable in the tubular holder. This stud slidestogether with the jaws and always occupies the same axial positionrelative to the jaws, so that it is very simple to equip the free end ofthis stud with the appropriate internal drive. Since the fastener headis axially immobilized, the internal drive also cannot be forced out ofthe corresponding recess of the fastener head. Thereby a relatively hightorque can be transmitted, even when the length of axial engagementoffered by the internal drive is relatively small.

In an advantageous alternative embodiment, it is proposed that the jawsbe squeezed resiliently toward each other by an O-ring inlaid in agroove on the outside circumference of the jaws in the region of theinwardly projecting toes, so that the jaws are pressed apart into openposition when in their position withdrawn from the holder. Thus there iscreated a structurally very simple variant, which on the one handgenerates the resilient effect and on the other hand createscorresponding retention of the jaws relative to the stud.

Another embodiment provides that compression springs are insertedbetween the jaws in the region of their free ends, so that the jaws,when in their position withdrawn from the holder, are forced apart intoopen position. By these features there is achieved practically the sameeffect, since the intended purpose in both embodiments is that the endsof the jaws protruding into the holder or the toes thereof remainconstantly pressed against the stud.

To achieve optimal retention of an inserted fastener head, it isproposed that the gripper-like parts each be extended over the entiresector region of the jaws. In this way the best possible all-aroundretention over the circumference of the fastener head is assured. Anoptimal and very simple construction is further achieved by providingtwo jaws extending approximately over an angular region of 180°.

Further features and special advantages according to the invention areexplained in further detail in the description given hereinafter withreference to the drawings, wherein:

FIG. 1 shows a section through a screwing element, wherein the jaws areillustrated in closed condition;

FIG. 2 shows the same screwing element, also illustrated in longitudinalsection, wherein the jaws are disposed in their open position;

FIG. 3 shows an elevation of a fastener, which can be set with ascrewing element according to the invention;

FIG. 4 and FIG. 6 to FIG. 9 each show longitudinal sections through ascrewing element according to FIGS. 1 and 2 with an inserted fastener,wherein various positions of the jaws inside the screwing element areillustrated;

FIG. 5 and FIG. 10 show sections through lines V—V and X—X respectivelyin FIGS. 4 and 9;

FIG. 11 shows a screwing element according to a different alternativeembodiment, wherein only the spring means for retention in open positionhave been changed compared with the embodiment according to FIGS. 1 and2.

Screwing element 1 according to FIGS. 1 and 2 comprises substantially atubular holder 2 and two jaws 3 and 4, and is used to accommodate afastener head 5 and to hold the same or to drive the same and thus todrive in a fastener 6. Fastener 6 is provided with an appropriate shank7 and a thread 8, and if necessary can also be equipped with a boringpart 9. Fastener head 5 has a shoulder 10, which is separated by lengthB from bearing face 11 of the head. In the example of a fastener shownhere, there is provided under shoulder 10 a portion 12, which is smallerin dimensions than shoulder 10 and for practical purposes is coveredalmost completely thereby. Portion 12 is equipped with a tool drive 13,which in the present case, for example, is hexagonal.

The purpose of screwing element 1 according to the invention is now tocreate a possibility of holding a fastener 6 securely and axiallyaligned during a boring and/or thread-forming process and/or during adriving-in process, and of transferring the appropriate torque from thescrewing element to fastener 6.

As already mentioned, two jaws 3 and 4 are present, although in thescope of the invention there can also be provided a plurality of jawsfor seizing fastener head 5 successively in circumferential direction.Jaws 3, 4 engage in tubular holder 2, and in cooperation therewith canbe closed or forced apart.

In their one end position (FIG. 2), jaws 3, 4 can be forced radiallyapart in order to insert a fastener head 5. Upon application of axialforce on jaws 3, 4 in the direction of arrow 14, jaws 3, 4 are forciblysqueezed toward each other in radial direction (position according toFIG. 1) by the mechanical interaction between holder 2 and jaws 3, 4. Atthe free end region of jaws 3, 4 there are provided incisions 15, 16,with which mechanical and/or frictional accommodation of a fastener head5 or else of portions of a fastener head can be achieved. In the case ofthe special screw according to FIG. 3, only the portion of fastener head5 forming shoulder 10 is accommodated in incisions 15, 16 of jaws 3, 4.At the free end of jaws 3, 4, adjoining the incisions or correspondingrecesses of other form, there are provided gripper-like parts 17, 18jutting outwardly toward the central axis, in order thereby to createthe possibility of engaging with fastener head 5 or portions thereof,such as shoulder 10, from behind by mechanical or frictional action.

Incisions 15, 16 on jaws 3, 4 correspond at least approximately to thecross section of the rim region of fastener head 5 to be seized or ofshoulder 10 formed thereon. On gripper-like parts 17, 18 there areprovided extensions 19, 20 of a tool for acting on fastener head 5 or ontool drive 13 in the region of portion 12.

As can be inferred from FIGS. 4 and 5 in this connection, fastener head5 is clamped securely between the two jaws 3 and 4 in the position ofscrewing element 1 as also illustrated in FIG. 1, wherein gripper-likeparts 17, 18 engage with shoulder 10 from behind or from underneath andbecome braced together with these gripper-like parts on tool drive 13 offastener head 5. In such a clamped form, fastener 6 can be held inclamped condition until it has been finally driven into the workpiece bythe screwing element, since even the one part of gripper-like parts 17,18 engaging with the one part of fastener head 5 from underneath cannotbear on the workpiece surface. If screwing element 1 is subsequentlyremoved in the direction of arrow 21 from fastener 6 or from fastenerhead 5 once fastener 5 [sic] has been set, jaws 3, 4 are pulled out ofholder 2 and ultimately occupy a position as illustrated in FIGS. 9 and10. In this position the two jaws 3 and 4 are forced sufficiently apartin their open position that fastener head 5 is released. The screwingelement can now be raised upward in the direction of arrow 21, thuspreparing it for accommodation of the next fastener 6, which merely hasto be pressed into the screwing element, with fastener head 5 leading.By virtue of the axial load on jaws 3, 4, these are pushed into holder2, so that jaws 3, 4 ultimately reach the closed position, in whichfastener head 5 is immobilized.

Jaws 3, 4 can therefore be pivoted mechanically and/or frictionally intotheir closed or open position by axial movement in tubular holder 2. Thesimplest embodiment is that in which mechanical retention is achieved inclosed position while not only mechanical locking by means of anappropriate spring but also frictional locking is provided in openposition. Jaws 3, 4 are therefore expediently spring-loaded in thedirection of their open position, wherein jaws 3, 4 in the examplesaccording to FIGS. 1 and 2 are squeezed resiliently toward each other byan O-ring 22 inlaid in a groove on the outer circumference of jaws 3, 4,specifically in the region of their ends protruding into holder 2.Thereby the jaws together with their ends projecting beyond the holderare forced apart into open position.

The only difference between the embodiment according to FIG. 11 and thealternative embodiment according to FIGS. 1 and 2 is that compressionsprings 23 are inserted between the jaws, in the region of their freeends, and so the jaws are forced apart to open position when in theirposition withdrawn from holder 2.

On the inside of holder 2 and on the outside of jaws 3, 4 there areprovided camming faces 25, 26 running at a sharp angle relative tocentral axis 24 of the screwing element, so that jaws 3, 4 are squeezedtoward each other when pushed axially inward in the direction of arrow14. Expediently, corresponding camming surfaces 25, 26 will be providedboth on holder 2 and on jaws 3, 4. It would also be conceivable,however, to form corresponding sharply tapering camming surfaces only onholder 2 or only on jaws 3, 4. For proper and smooth function, however,it is practical to form appropriate camming faces which correspond toeach other on two regions adjacent to one another.

At their ends protruding into tubular holder 2, jaws 3, 4 are providedwith radially inwardly directed toes 27, 28, which engage in a radiallycircumferential groove 29 of a stud 30 which is axially slidable inscrewing element 1. At its portion 31 adjoining groove 29 for engagementof toes 27, 28, stud 30 is adapted to the inside cross section of jaws3, 4 in closed condition. Portion 31, which forms the transition betweengroove 29 and end part 32 of stud 30, advantageously has sphericallyconvex shape, and the inside regions of jaws 3, 4 are also shapedcorrespondingly. For practical purposes, therefore, a kind ofball-and-socket joint is created between stud 30 and jaws 3, 4, and sostud and jaws can slide optimally over each other, thus ensuring optimalpivotability from the closed position of jaws 3, 4 to the open positionthereof.

Stud 30 together with the jaws is positioned in the direction of axis 24by application of appropriate axial pressure and/or tension on jaws 3,4. At its end protruding into holder 2, stud 30 is provided withcircumferential grooves 33 and 34, in which there can engage a pin 36spring-loaded by an O-ring 35, for example, or an appropriate ball.Spring-loaded pin 36 thus engages in one of the grooves 33 and 34 whenstud 30 is at least in the region of its two end positions, thusadditionally ensuring further frictional retention of stud 30 and thusof the jaws in the two end positions. Instead of spring-loaded pin 36,it would of course also be possible to provide appropriatelyspring-loaded balls or the like, which engage in appropriatelycircumferential groove 33 or 34.

At the free end, stud 30 is provided with a circumferential shoulder 37,which is larger in diameter than the portion of stud 30 provided withthe two grooves 33 and 34. A ball 38, which protrudes partly into theregion of bore 39 in holder 2 and thus prevents stud 30 from beingcompletely pulled out, is held secured against axial displacement inholder 2. Circumferential shoulder 37 is prevented from further shiftingby ball 38 protruding into bore 39.

However, when a sleeve 40 which fits over tubular holder 2 is raisedagainst the force of a helical spring 41, ball 38 is also released to acertain extent, and so stud 30 can be completely withdrawn from bore 39.Thereby it is also easily possible to replace jaws 3, 4 and stud 30 andalso to disassemble and reassemble them for other purposes.

Gripper-like parts 17, 18 expediently extend over the entire sectorregion of jaws 3, 4. It is also entirely conceivable, however, toprovide here only individually projecting parts or ridges, which formgripper-like parts 17, 18. Instead of gripper-like parts 17, 18 whichjut outwardly toward the central axis, it would also be possible toprovide openings or profiled structures directed away from the centralaxis, if correspondingly shaped fasteners 6 or correspondingly shapedfastener heads 5 are to be seized. In this case, appropriatelyprojecting raised structures, pegs or the like would then be provided onfastener heads 5. It would also be conceivable for the raisedstructures, pegs or the like to project beyond the circumference of ashoulder 10 on fastener head 5.

In the foregoing description, it was mentioned that extensions of a tooldrive are provided on gripper-like parts 17, 18 or on correspondingopenings or profiled structures. Within the scope of the invention, itis also possible to form such extensions of a tool drive in the regionof incisions 15, 16, recesses or the like or adjoining these but offsetin axial direction. Naturally it would also be conceivable to providetwo or more incisions 15, 16 on the jaws as viewed in axial direction,if a fastener head 5 were to be provided, for example, with two or moreshoulders 10 disposed at successive intervals in axial direction.

In this connection, it would be further conceivable to provide thegripper-like parts or pegs directed appropriately toward the centralaxis or openings or profiled structures directed away from this centralaxis in the immediate region of incisions 15, 16, so that then evenfasteners 6 provided only with a kind of shoulder 10, on whichprojections or depressions or pegs and holes are provided directly, canbe held on fastener head 5. In such an embodiment, the jaws would thencorrespond to the form of shoulder 10 of fastener head 5, and mechanicaland/or frictional locking would be achieved by the mutually engagingraised structures and projections. In this case also a holder which canbe fixed as viewed in axial direction can be provided for fastener head5 in the screwing element. If gripper-like parts 17, 18 are present andthese parts engage with shoulder 10 of a fastener head 5 from behind,then a corresponding portion 12 must be present in some form in order tocreate the space defined by length B between the bearing face offastener head 5 and the beginning of shoulder 10.

Instead of portion 12, it is naturally also possible to insert at thisplace an appropriate washer with diameter smaller than that of shoulder10, so that a fastener head can be clamped in a screwing elementaccording to the invention in this case also.

Precisely in such an embodiment, although also in embodiments with aone-piece screw head as illustrated in FIG. 3, it is conceivable toform, at the center between jaws 3, 4, a tool for an internal drive inaddition to jaws 3, 4 holding fastener head 5. In this case acorresponding internal drive would be formed in fastener head 5, and sothe corresponding tool can also be formed or disposed, for example, atthe free end of stud 30, which is slidable in tubular holder 2.

In the foregoing description there have been explained practicalexamples in which jaws 3 and 4 are axially slidable in a tubular holder2, and specifically from an open position to a closed position, whereinmechanical and/or frictional positioning of jaws 3, 4—possibly togetherwith a corresponding stud 30—is also achieved by the axial slidingprocess. Within the scope of the invention, however, it is alsoconceivable to dispose jaws 3, 4 in a different embodiment of a tubularholder 2, wherein jaws 3, 4 would then no longer be axially slidablerelative to holder 2. The open position would then be brought aboutsolely by application of radial force or by loosening jaws 3, 4 topermit radial mobility, or jaws 3, 4 could be brought into closedposition by appropriate turning of, for example, sleeve parts. In thisconnection it would also be conceivable to hold jaws 3, 4 axiallyimmovably relative to a spud 43, which can be inserted in a screwingdevice, wherein tubular holder 2 could then be withdrawn exactly in thedirection of arrow 14, in order thereby to pivot jaws 3, 4 into openposition. From the structural viewpoint, therefore, extremely diverseembodiments are possible.

What is claimed is:
 1. A screwing element for holding and for forcibly turning a fastener (6), with a plurality of jaws (3, 4), which are disposed in succession in circumferential direction for seizing the fastener (6), where the jaws (3, 4) engage in a tubular holder (2) and, in combination with this holder (2), in a first end position can be forced radially apart for the purpose of holding the fastener, and in a second end position can be radially squeezed together by mechanical action of the holder (2) in response to application of axial and/or radial force, characterized in that incisions (15, 16) or recesses are formed on the free end region of the jaws (3, 4) for mechanical and/or frictional accommodation of a fastener head (5), in that gripper-like parts (17, 18) jutting outwardly toward the central axis (24) or directed away therefrom are formed on the free end of the jaws (3, 4), adjoining the incisions (15, 16) or recesses, for the purpose of additional mechanical and/or frictional seizing of portions of the fastener head (5), and in that, on the inside of the holder (2) and/or on the outside surface of the jaws (3, 4), there are formed camming surfaces (25, 26) which taper sharply toward the central axis (24), wherein the jaws (3, 4) can be squeezed together by the camming surfaces (25, 26) in response to being forced axially into the holder (2).
 2. A screwing element according to claim 1, characterized in that sharply tapering camming surfaces (25, 26) are provided on both the holder (2) and on the jaws (3, 4).
 3. A screwing element for holding and for forcibly turning a fastener (6), with a plurality of jaws (3, 4), which are disposed in succession in circumferential direction for seizing the fastener (6), where the jaws (3, 4) engage in a tubular holder (2) and, in combination with this holder (2), in a first end position can be forced radially apart for the purpose of holding the fastener, and in a second end position can be radially squeezed together by mechanical action of the holder (2) in response to application of axial and/or radial force, characterized in that incisions (15, 16) or recesses are formed on the free end region of the jaws (3, 4) for mechanical and/or frictional accommodation of a fastener head (5), in that gripper-like parts (17, 18) jutting outwardly toward the central axis (24) or directed away therefrom are formed on the free end of the jaws (3, 4), adjoining the incisions (15, 16) or recesses, for the purpose of additional mechanical and/or frictional seizing of portions of the fastener head (5), and in that the jaws (3, 4) are provided at their ends protruding into the tubular holder (2) with radially inwardly directed toes (27, 28), which engage in a radially circumferential groove (29) of a stud (30) that is axially slidable in the screwing element (1) and can be fixed in a plurality of latching positions, wherein this stud (30) can be positioned together with the jaws (3, 4) by the action of axial pushing or pulling thereon.
 4. A screwing element according to claim 3, characterized in that the stud (30) can be fixed latchingly at least in the two end positions of the jaws (3, 4).
 5. A screwing element according to claim 3 characterized in that the stud (30) is provided with at least two latching positions formed by circumferential grooves (33, 34), wherein a spring-loaded pin (36) or a ball which engages in the corresponding circumferential groove (33, 34) is held on the tubular holder (2).
 6. A screwing element according to claim 3, characterized in that the stud (30) is adapted on its portion (31) adjoining the groove (29) for engagement with the toes (27, 28) formed on the jaws (3, 4) to the inside cross section of the jaws (3, 4) in closed condition, wherein the transition between the groove (29) and the end part (32) of the stud (30) and the corresponding regions of the jaws (3, 4) are spherically convex.
 7. A screwing element for holding and for forcibly turning a fastener (6), with a plurality of jaws (3, 4), which are disposed in succession in circumferential direction for seizing the fastener (6), where the jaws (3, 4) engage in a tubular holder (2) and, in combination with this holder (2), in a first end position can be forced radially apart for the purpose of holding the fastener, and in a second end position can be radially squeezed together by mechanical action of the holder (2) in response to application of axial and/or radial force, characterized in that incisions (15, 16) or recesses are formed on the free end region of the jaws (3, 4) for mechanical and/or frictional accommodation of a fastener head (5), in that gripper-like parts (17, 18) jutting outwardly toward the central axis (24) or directed away therefrom are formed on the free end of the jaws (3, 4), adjoining the incisions (15, 16) or recesses, for the purpose of additional mechanical and/or frictional seizing of portions of the fastener head (5), and in that the tool for an internal drive is formed or disposed at the free end of the stud (30) which is slidable in the tubular holder (2).
 8. A screwing element for holding and for forcibly turning a fastener (6), with a plurality of jaws (3, 4), which are disposed in succession in circumferential direction for seizing the fastener (6), where the jaws (3, 4) engage in a tubular holder (2) and, in combination with this holder (2), in a first end position can be forced radially apart for the purpose of holding the fastener, and in a second end position can be radially squeezed together by mechanical action of the holder (2) in response to application of axial and/or radial force, characterized in that incisions (15, 16) or recesses are formed on the free end region of the jaws (3, 4) for mechanical and/or frictional accommodation of a fastener head (5), in that gripper-like parts (17, 18) jutting outwardly toward the central axis (24) or directed away therefrom are formed on the free end of the jaws (3, 4), adjoining the incisions (15, 16) or recesses, for the purpose of additional mechanical and/or frictional seizing of portions of the fastener head (5), and in that the jaws (3, 4) are forced resiliently toward each other by an O-ring (22) inlaid in a groove on the outside circumference of the jaws (3, 4) in the region of the inwardly projecting toes (27, 28), so that the jaws (3, 4) are pressed apart into open position when in their position withdrawn from the holder.
 9. A screwing element for holding and for forcibly turning a fastener (6), with a plurality of jaws (3, 4), which are disposed in succession in circumferential direction for seizing the fastener (6), where the jaws (3, 4) engage in a tubular holder (2) and, in combination with this holder (2), in a first end position can be forced radially apart for the purpose of holding the fastener, and in a second end position can be radially squeezed together by mechanical action of the holder (2) in response to application of axial and/or radial force, characterized in that incisions (15, 16) or recesses are formed on the free end region of the jaws (3, 4) for mechanical and/or frictional accommodation of a fastener head (5), in that gripper-like parts (17, 18) jutting outwardly toward the central axis (24) or directed away therefrom are formed on the free end of the jaws (3, 4), adjoining the incisions (15, 16) or recesses, for the purpose of additional mechanical and/or frictional seizing of portions of the fastener head (5), and in that compression springs (23) are inserted between the jaws (3, 4) in the region of their free ends, so that the jaws (3, 4) when in their position withdrawn from the holder (2), are forced apart into open position.
 10. A screwing element for holding and for forcibly turning a fastener (6), with a plurality of jaws (3, 4), which are disposed in succession in circumferential direction for seizing the fastener (6), where the jaws (3, 4) engage in a tubular holder (2) and, in combination with this holder (2), in a first end position can be forced radially apart for the purpose of holding the fastener, and in a second end position can be radially squeezed together by mechanical action of the holder (2) in response to application of axial and/or radial force, characterized in that incisions (15, 16) or recesses are formed on the free end region of the jaws (3, 4) for mechanical and/or frictional accommodation of a fastener head (5), in that gripper-like parts (17, 18) jutting outwardly toward the central axis (24) or directed away therefrom are formed on the free end of the jaws (3, 4), adjoining the incisions (15, 16) or recesses, for the purpose of additional mechanical and/or frictional seizing of portions of the fastener head (5), and in that there are provided two jaws (3, 4) extending approximately over an angular region of 180°. 